1. Field of the Invention
This invention relates to a profile-measuring light probe, and more particularly, to improvements in a light probe for measuring a profile of a subject to be measured in non-contact therewith by optical means through the utilization of a change in reflection factor in the proximity of a critical angle of a light. The inventive light probe is suitable for use as a probe in a coordinate measuring machine.
2. Description of the Prior Art
There have been popularized coordinate measuring machines, in each of which a subject to be measured, which is rested on a mount, and a probe supported on a main body of machine are relatively moved in a tridimensional manner by a moving mechanism, whereby a relative movement value between the probe and the subject to be measured is detected. This movement value is processed in a predetermined manner by a data processing unit, so that a height, a profile and the like of the subject can be measured.
The probes for the coordinate measuring machines, have been mainly contact-type probes. However, as the subjects to be measured come to cover parts made of thin plastics, clay models and the like, necessity has been voiced for the development of non-contact type probe.
As a consequence, there have heretofore been proposed various non-contact type probes using optical means. However, there has been presented such a problem that the non-contact type probe is coarse in resolution as compared with the contact-type probe.
To improve the resolution, there has been proposed a probe using a critical angle prism utilizing a change in an internal reflection factor in the proximity of a critical angle when the total reflection occurs in a prism. For example, in Japanese Utility Model Kokai (Laid-Open) No. 6707/1986, there is disclosed such a probe that, to improve the resolution, four internal reflections are performed in an critical angle prism.
However, since a light from the subject to be measured is collimated by an objective lens and made to fall directly into a prism, a large critical angle prism with high accuracy is needed, and such a disadvantage is presented that optical parts are expensive. Furthermore, since the critical angle is varied in accordance with the refractive index, such a problem is presented that the refractive index should be accurately measured during the manufacture of the prism. Further, since a change in the distribution of quantity of light in an optical system of the probe to a change in profile of the subject to be measured, i.e. the sensitivity is not yet satisfactorily large, an electric amplitude should be increased to make the resolution fine, and such a problem is presented that electrical noises tend to mix thereinto.